Elements Of Beaked Whale Anatomy And Diving

2y ago
9 Views
2 Downloads
1.67 MB
21 Pages
Last View : 20d ago
Last Download : 2m ago
Upload by : Julius Prosser
Transcription

J. CETACEAN RES. MANAGE. 7(3):189–209, 2006189Elements of beaked whale anatomy and diving physiology andsome hypothetical causes of sonar-related strandingS.A. ROMMEL*, A.M. COSTIDIS*, A. FERNÁNDEZ , P.D. JEPSON#, D.A. PABST , W.A. MCLELLAN , D.S. HOUSER**,T.W. CRANFORD , A.L. VAN HELDEN , D.M. ALLEN AND N.B. BARROS Contact e-mail: sentiel.rommel@myfwc.comABSTRACTA number of mass strandings of beaked whales have in recent decades been temporally and spatially coincident with military activitiesinvolving the use of midrange sonar. The social behaviour of beaked whales is poorly known, it can be inferred from strandings and someevidence of at-sea sightings. It is believed that some beaked whale species have social organisation at some scale; however most strandingsare of individuals, suggesting that they spend at least some part of their life alone. Thus, the occurrence of unusual mass strandings of beakedwhales is of particular importance. In contrast to some earlier reports, the most deleterious effect that sonar may have on beaked whalesmay not be trauma to the auditory system as a direct result of ensonification. Evidence now suggests that the most serious effect is theevolution of gas bubbles in tissues, driven by behaviourally altered dive profiles (e.g. extended surface intervals) or directly fromensonification. It has been predicted that the tissues of beaked whales are supersaturated with nitrogen gas on ascent due to thecharacteristics of their deep-diving behaviour. The lesions observed in beaked whales that mass stranded in the Canary Islands in 2002 areconsistent with, but not diagnostic of, decompression sickness. These lesions included gas and fat emboli and diffuse multiorganhaemorrhage. This review describes what is known about beaked whale anatomy and physiology and discusses mechanisms that may haveled to beaked whale mass strandings that were induced by anthropogenic sonar.Beaked whale morphology is illustrated using Cuvier’s beaked whale as the subject of the review. As so little is known about the anatomyand physiology of beaked whales, the morphologies of a relatively well-studied delphinid, the bottlenose dolphin and a well-studiedterrestrial mammal, the domestic dog are heavily drawn on.KEYWORDS: BEAKED WHALES; STRANDINGS; BOTTLENOSE DOLPHIN; ACOUSTICS; DIVING; RESPIRATION; NOISE;METABOLISMINTRODUCTIONStrandings of beaked whales and other cetaceans that aretemporally and spatially coincident with military activitiesinvolving the use of mid-frequency (1-20kHz) active sonarshave become an important issue in recent years (Nascetti etal., 1997; Frantzis, 1998; Anon., 2001; 2002; Balcomb andClaridge, 2001; Jepson et al., 2003; Fernández, 2004;Fernández et al., 2004; 2005; Crum et al., 2005). Thisreview describes the relevant aspects of beaked whaleanatomy and physiology and discusses mechanisms thatmay have led to the mass strandings of beaked whalesassociated with the use of powerful sonar. The anatomy andphysiology of marine mammals are not as well studied asare those of domestic mammals (Pabst et al., 1999) andwithin the cetacean family of species even less is knownabout the beaked whales than about the more commondelphinids (e.g. the bottlenose dolphin, Tursiops truncatus).Furthermore, many of the morphological and physiologicalprinciples that are applied to pathophysiological evaluationsof marine mammals were developed on small terrestrialmammals such as mice, rats and guinea pigs (e.g. Anon.,2001). Predictions and interpretations of functionalmorphology, physiology and pathophysiology musttherefore be handled cautiously when applied to therelatively large diving mammals (Fig. 1). Interpolation is a* Floridarelatively accurate procedure, but extrapolation, particularlywhen it involves several orders of magnitude in size, is lessso (K. Schmidt-Nielsen, pers. comm. to S. Rommel).Beaked whales are considered deep divers based on theirfeeding habits, deep-water distribution and dive times(Heyning, 1989b; Hooker and Baird, 1999; Mead, 2002).Observations from time-depth recorders on some beakedFig. 1. Body size, expressed as weight and length for a variety ofmammals. Marine mammals are large when compared to most othermammals and beaked whales are relatively large marine mammals.Fish and Wildlife Conservation Commission, Fish and Wildlife Research Institute, Marine Mammal Pathobiology Lab, 3700 54th Ave. South,St. Petersburg, FL 33711, USA. Unit of Histology and Pathology, Institute for Animal Health, Veterinary School, Universidad de Las Palmas de Gran Canaria, Montaña Cardones,Arucas, Las Palmas, Canary Islands, Spain.# Institute of Zoology, Zoological Society of London, Regent’s Park, London, NW1 4RY, UK. Department of Biology and Marine Biology, University of North Carolina Wilmington, Wilmington, NC 28403, USA.** BIOMIMETICA, 7951 Shantung Drive Santee, CA 92071, USA. Department of Biology, San Diego State University, San Diego CA, USA. Museum of New Zealand Te Papa Tongarewa, Wellington, New Zealand. National Museum of Natural History, Smithsonian Institution, Washington, DC, 20560, USA. Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, FL 34236 USA.

190ROMMEL et al.: SOME HYPOTHETICAL CAUSES OF SONAR-RELATED STRANDINGwhales have documented dives to 1,267m and submergencetimes of up to 70min (Baird et al., 2004; Hooker and Baird,1999; Johnson et al., 2004). Notably, beaked whales spendmost of their time (more than 80%) at depth, typicallysurfacing for short intervals of one hour or less. Virtually nophysiological information on beaked whales exists andinformation on any cetacean larger than the bottlenosedolphin is rare. Given this paucity of data this review relieson information obtained from both terrestrial mammals andother marine mammal species. In particular it draws heavilyfrom the morphology of a well-studied terrestrial mammal,the domestic dog (Canis familiaris) and a relatively wellstudied cetacean, the bottlenose dolphin, referred to hereinas Tursiops (Fig. 2). Beaked whale morphology is illustratedusing Cuvier’s beaked whale (Ziphius cavirostris), furtherreferred to as Ziphius. Ziphius, based on stranding records(they are rarely identified at sea), is the most cosmopolitanof the 21 beaked whale species (within 6 genera: Berardius,Hyperoodon, Indopacetus, Mesoplodon, Tasmacetus andZiphius) (Baird et al., 2004; Dalebout and Baker, 2001;Mead, 2002; Rice, 1998).ANATOMY/PHYSIOLOGYBefore considering the potential mechanism by whichsounds may affect beaked whales, it is important to reviewwhat is known and can be inferred of their anatomy andphysiology.External morphologyAside from dentition and conspecific scarring betweenmales, there are few external morphological differencesbetween the genders of Ziphius (Mead, 2002). The head isrelatively smooth (Figs 2 and 3) and the average adult totalbody length is 6.1m (Heyning, 2002). The throats of allbeaked whales have a bilaterally paired set of groovesassociated with suction feeding (Heyning and Mead, 1996).Ziphius bodies are robust and torpedo-like in shape, withsmall dorsal fins approximately 1/3 of the distance from thetail to the snout. The relatively short flippers can be tuckedinto shallow depressions of the body wall (Heyning,2002).Specialised lipidsMarine mammals have superficial lipid layers calledblubber (Fig. 3). Blubber in non-cetaceans is similar to thesubcutaneous lipid found in terrestrial mammals; in contrast,the blubber of cetaceans is a thickened, adipose-richhypodermis (reviewed in Pabst et al., 1999; Struntz et al.,2004). Cetacean blubber makes up a substantial proportion(15-55%) of the total body weight (Koopman et al., 2002;McLellan et al., 2002) and the lipid content can varydepending upon the species and the sample site (Koopmanet al., 2003a). Blubber is richly vascularised to facilitateheat loss (Kanwisher and Sundes, 1966; Parry, 1949) and iseasily bruised by mechanical insult. Since blubber has adensity that can be different from those of water and muscle,it may respond to ensonification differently, particularly ifconditions of vascularisation (i.e. volume and temperatureof blood) vary. The roles blubber (and other lipids) may playin whole-body acoustics should be the subject of furtherresearch.As in other odontocetes, the hollowed jaw is surroundedby acoustic lipids1, although the beaked whale acousticlipids are chemically different from those of otherodontocetes (Koopman et al., 2003b). These acoustic lipidsconduct sound to the pterygoid and peribullar sinuses andears (Koopman et al., 2003a; Norris and Harvey, 1974;Wartzog and Ketten, 1999) and may function as anacoustical amplifier, similar to the pinnae of terrestrial1Evidence from anatomical, morphological, biochemical andbehavioural studies all support the role of the melon and mandibularlipids in the transmission and reception of sound by odontocetes(Norris and Harvey, 1974; Koopman et al., 2003b; Ketten et al.,2001;Varanasi et al., 1975; Wartzog and Ketten, 1999). Thus, these fatsare collectively referred to here as the ‘acoustic lipids’.Fig. 2. The skeleton of a Cuvier’s beaked whale, (a) compared to selected marine mammal skeletons: sea otter, Enhydralutris (b); harbour seal, Phoca vitulina (c), Florida manatee, Trichechus manatus latirostris (d); California sea lion,Zalophus californianus (e); bottlenose dolphin (f) and the domestic dog, Canis familiaris (g). Each skeleton was scaledproportionately to the beaked whale. The Ziphius skeleton was drawn from photographs of Smithsonian Institutionskeleton #504094 and from photographs courtesy of A. van Helden; other skeletons were re-drawn from Rommel andReynolds (2002).

J. CETACEAN RES. MANAGE. 7(3):189–209, 2006191Fig. 3. The external morphology of a Cuvier’s beaked whale (a) compared with that of the bottlenose dolphin (b). Whencompared to terrestrial mammals, Odontocetes have extensive and atypical fat deposits and fat emboli have beenimplicated in some beaked whale mass strandings; thus, their potential sources (such as well-vascularised fat deposits)are of special interest. Skin lipids (or blubber) perform several functions: for example, buoyancy, streamlining andthermoregulation. (c) This drawing illustrates the thickness of the blubber of a dolphin along the midline of the body.(d-f) Odontocetes have specialised acoustic lipids, represented by contours in f, which are found in the melon and lowerjaw. These lipids have physical characteristics that guide sound preferentially.mammals (Cranford et al., 2003). The ziphiid melon issimilar in size, shape and position to that of otherodontocetes (Heyning, 1989b), but Koopman et al. (2003b)have shown that like the jaw fat, the acoustic lipids of theziphiid melon are also chemically different. This suggestspotential differences in sound propagation properties andperhaps in response to anthropogenic ensonification. Thus,understanding the role and composition of acoustic lipidsmay be important in interpreting lesions in mass strandedbeaked whales.Extensive fat deposits are also found in the skeleton. Mostcetacean bones are constructed of spongy, cancellous bone,with a thin or absent cortex (de Buffrenil and Schoevaert,1988). Like the fatty marrow found in terrestrial mammalbones, the medullae of cetacean bones are rich in lipids andup to 50% of the wet-weight of a cetacean skeleton may beattributed to lipid. Since it has been demonstrated thatindividual lipids within the same, as well as different, partsof the cetacean body may be structurally distinct, it may beof value to analyse the composition of fat emboli todetermine if the sources are from general or specific lipiddeposits. Thus, lipid characterisation of fat emboli may helppinpoint the source of lipids and therefore the site of injury.The skeletal systemThere is a pronounced sexual dimorphism in the skulls ofZiphius; the species name (cavirostris) is derived from thedeep excavation (prenarial basin) on the rostrum that occursin mature males (Heyning, 1989a; Heyning, 2002; Kernan,1918; Omura et al., 1955). The bones of male beaked whale

192ROMMEL et al.: SOME HYPOTHETICAL CAUSES OF SONAR-RELATED STRANDINGrostra (the premaxillaries, maxillaries and vomer) maybecome densely ossified (in the extreme, up to 2.6g cm23 inBlainville’s beaked whale, Mesoplodon densirostris),thought to be an adaptation for conspecific aggression (deBuffrenil and Zyberberg, 2000; MacLeod, 2002). Bothgenders have homodont dentition (teeth are all the sameshape) and a caudally hollowed, lipid-filled, lower jaw, asdo other odontocetes.The premaxillary, maxillary and vomer bones areelongated rostrally and the premaxillaries and maxillariesare also extended dorsocaudally over the frontal bones (Fig.4b; telescoping, Miller, 1923). The narial passages areessentially vertical in all cetaceans and the nasal bones arelocated at the vertex of the skull, dorsal to the braincase. InTursiops, the nasal bones are relatively small vestiges thatlie in shallow depressions of the frontal bones (Rommel,1990). Conversely, the nasal bones of beaked whales arerobust and are part of the prominent rostral projections ofthe skull apex (Fig. 4; Kernan, 1918; Heyning, 1989a).Odontocetes have larger, more complex pterygoid bonesthan terrestrial mammals. In delphinids, the pterygoid andpalatine bones form thin, almost delicate, medial and lateralwalls lining the bilaterally paired pterygoid sinuses. Thepterygoid sinuses of Tursiops are narrow structures that areconstrained by the margins of the pterygoid bones. Incontrast, the pterygoid bones of beaked whales are thick androbust (Figs 4 and 5) and their pterygoid sinuses are verylarge (measured by Scholander (1940) each to beapproximately a litre in volume in the northern bottlenosewhale, Hyperodon ampullatus). Beaked whale (andphyseteroid) pterygoid sinuses lack bony lateral laminae(Fraser and Purves, 1960). These morphologicalcharacteristics of the pterygoid region imply differences inmechanical function and perhaps response to ensonificationby anthropogenic sonar, and thus may be important ininterpreting lesions found in beaked whales.In most mammals, there is a temporal ‘bone’, which is acompound structure made up of separate bony elementsand/or ossification centres (Nickel et al., 1986). In manymammals, the squamosal bone is firmly ankylosed to theperiotic (petrosal, petrous), tympanic (or parts thereof) andmastoid bones to form the temporal bone (Kent and Miller,1997). However, this is not the case in fully aquatic marinemammals (cetaceans and sirenians), where the squamosal,periotic and tympanic bones (there is some controversy overthe nature of the mastoid as a separate ‘bone’) remainseparate (Rommel, 1990; Rommel et al., 2002). Unlike theskulls of most other mammals in which the periotic bonesare part of the inner wall of the braincase, the cetaceantympano-periotic bones are excluded from the braincase(Fig. 5; Fraser and Purves, 1960; Geisler and Lou, 1998).The beaked whale tympano-periotic is a dense, compactbone (as in other cetaceans), whereas its mastoid process(caudal process of the tympanic bulla) is trabecular2 (likemost other cetacean skull bones). The Ziphius mastoidprocess, unlike that of the delphinids (and some otherbeaked whales), is relatively large and interdigitates with themastoid process of the squamosal bone (Fraser and Purves,1960).The beaked whale basioccipital bone is relativelymassive, with thick ventrolateral crests, in contrast to thebasioccipital crests in delphinids, which are relatively tallbut thin and laterally cupped (Fig. 5). In odontocetes, thereare large, vascularised air spaces (peribullar sinuses)between the tympano-periotics and basioccipital crests. In2A trabecular mastoid is also observed in some physeteroids.Tursiops, the pathway from the braincase for the 7th and 8thcranial nerves is a short (parallel to these nerves), opencranial hiatus (Rommel, 1990) bordered by relatively thinbones. In Ziphius, this path is a narrow, relatively longchannel through the basioccipital bones (Fig. 5). It is similarin position, but not homologous to the internal acoustic(auditory) meatus of terrestrial mammals. The morphologyof the pterygoid and basioccipital bones and the size andorientation of the cranial hiatus likely contribute todifferences in acoustical properties and mechanicalcompliance of the beaked whale skull. These bonystructures are therefore of potential importance in the effectsof acoustical resonance.The vertebral column supports the head, trunk and tail(Figs 2 and 6). In Tursiops the first two cervical vertebraeare fused, but the rest are typically unfused (Rommel, 1990);in contrast, the first four cervicals of Ziphius are fused.There is more individual variation in the numbers ofvertebrae in each of the postcervical regions of cetaceansthan in the dog. The numbers of thoracic vertebrae varybetween Tursiops and Ziphius: there are 12-14 thoracics inTursiops and 9-11 in Ziphius. In cetaceans, the lumbarregion has more vertebrae than that of many terrestrialmammals, significantly more so in Tursiops (16-19) than inZiphius (7-9), however the lumbar section of Ziphius isgreater in length than that of Tursiops. As in all othercetaceans, there has been a substantial reduction of thepelvic girdle and subsequent elimination (by definition) ofthe sacral vertebrae. The caudal regions have also beenelongated to varying degrees. The vertebral formula thatsummarises the range of these numbers for Tursiops isC7:T12-14:L16-19:S0:Ca24-28 and for Ziphius is C7:T911:L7-9:S0:Ca19-22 (Figs 6b and 6c).There is a bony channel, the neural canal (Fig. 6b),located within the neural arches, along the dorsal aspects ofthe vertebral bodies of the spinal column. In most mammalsthe neural canal is slightly larger than the enclosed spinalcord (Nickel et al., 1986). In contrast, some marinemammals (e.g. seals, cetaceans and manatees) haveconsiderably larger (i.e. 10-30X) neural canals, whichaccommodate the relatively large masses of epiduralvasculature and/or fat (Rommel and Lowenstein, 2001;Rommel and Reynolds, 2002; Rommel et al., 1993;Tomlinson, 1964; Walmsley, 1938). These epidural vascularmasses are largest in deeper diving cetaceans (Ommanney,1932; Vogl and Fisher, 1981; Vogl and Fisher, 1982; S.Rommel, pers. obs. in beaked whales and sperm whales). Inthe tail, there is a second bony channel formed by thechevron bones, which is located on the ventral aspect of thespinal column (Pabst, 1990; Rommel, 1990). The chevronbones form a chevron (hemal) canal, which encompasses avascular countercurrent heat exchanger, the caudal vascularbundle (Figs 6b and 6c; Rommel and Lowenstein, 2001).The ribs of cetaceans are positioned at a more acute angleto the long axis of the body than those of terrestrialmammals in order to accommodate decreases in lungvolume with depth. The odontocete thorax hascostovertebral joints that allow a large swing of the vertebralribs, which substantially increases the mobility of the ribcage (Rommel, 1990). This extreme mobility of the rib cagepresumably accommodates the lung collapse thataccompanies depth-related pressure changes (Ridgway andHoward, 1979). In cetaceans, the single-headed ribattachment is at the distal tip of the relatively widetransverse processes instead of the centrum as it is in othermammals (Rommel, 1990). In contrast to Tursiops, in which4-5 ribs are double-headed, 7 of the ribs in Ziphius are

J. CETACEAN RES. MANAGE. 7(3):189–209, 2006193Fig. 4. Bones of the domestic dog skull (a) compared with a schematic illustration (b) showing telescoping in odontocetes and with theskull bones of Tursiops (c) and Ziphius (d). Telescoping refers to the elongation of the rostral elements (both fore and aft in the caseof the premaxillary and maxillary bones), the dorso-rostral movement of the caudal elements (particularly the supraoccipital bone)and the overlapping of the margins of several bones. One major consequence of telescoping is the displacement of the external nares(and the associated nasal bones) to the dorsal apex of the skull. One of the most striking differences between the Tursiops and Ziphiusskulls is the relatively massive pterygoid bones of the latter. The nasal bones of beaked whales are more prominent and extend fromthe skull apex. Tursiops has extensive tooth rows; in contrast Ziphius has no maxillary teeth. The dog and Tursiops skulls are adaptedfrom Rommel et al. (2002). The Ziphius skull was drawn from skulls S-95-Zc-21 and SWF-Zc-8681-B (courtesy of N. Barros and D.Odell), from photographs of Smithsonian Institution skull #504094 and from photographs courtesy of A. van Helden and D. Allen.double-headed. This arrangement may contribute to thefunction (e.g. mechanical support or pumping action) ofthoracic retia mirabilia located on the dorsal aspect of thethoracic cavity (Fig. 7) by placing the costovertebral hingescloser to the lateral margins of the retia. Delphinids havebony sternal ribs, whereas those of beaked whales arecartilaginous. The sternum of Tursiops is composed of 3-4sternabrae, whereas that of Ziphius is 5-6. Thesemorphological differences might produce differentdynamics during changes of the thorax in response to divingand thus alter some of the physical properties of the airfilled spaces. This is an area requiring further research,particularly because we do not know at what depth beakedwhale lungs collapse.The air-filled spacesIn addition to the flexible rib cage, cetacean respiratorysystems possess morphological specialisations supportive ofan aquatic lifestyle (Pabst et al., 1999). Thesespecialisations involve the blowhole, the air spaces of thehead, the larynx and the terminal airways of the lung.The single blowhole (external naris) of most odontocetesis at the top of the head (Fig. 7). During submergence, theair passages are closed tightly by the action of the nasal plugthat covers the internal respiratory openings (Fig. 8). Thenasal plug sits tightly against the superior bony nares andseals the entrance to the air passages when the nasal plugmuscles are relaxed (Lawrence and Schevill, 1956; Mead,1975).

194ROMMEL et al.: SOME HYPOTHETICAL CAUSES OF SONAR-RELATED STRANDINGFig. 5. Cross-sections of the skulls of Tursiops (a) and Ziphius (b). The cross sections (at the level of the ear) are scaled to have similarareas of braincase. In Tursiops, the pathway out of the braincase for the VIIth &VIIIth cranial nerves is a short open cranial hiatus(Rommel, 1990) bordered by relatively thin bones, whereas in Ziphius it is a narrow, relatively long channel. The ziphiid basioccipitalbones are relatively massive with thick ventrolateral crests; in contrast, delphinid basioccipital bones are relatively long and tall, butthin and laterally cupped. Note that in contrast to the Ziphius calf cross-section, the adult head would have a greater amount of boneand the brain size would be different. The cross section of an adult Tursiops is after Chapla and Rommel (2003) and that of Ziphiusis after a scan of a calf (courtesy of T. Cranford). Midsagittal sections of an adult Tursiops (c; after Rommel, 1990) and an adultZiphius (d; drawn from photographs of a sectioned skull at the Museum of New Zealand Te Papa Tongarewa).The anatomy of the blowhole vestibule and its associatedair sacs varies within, as well as between, odontocetespecies (Mead, 1975), yet the overall echolocating functionsare believed to be similar. In Ziphius, the vestibule is longerand more horizontal than in Tursiops (Fig. 8) and Ziphiushas no vestibular sacs, no rostral components of thenasofrontal sacs and the right caudal component of the nasalsacs extends up and over the apex of the skull (Heyning,1989a). In some Ziphius males, there are relatively small,left (caudal) nasal sacs, which are vestigial or absent infemales (Heyning, 1989b). The premaxillary sacs, which lieon the dorsal aspect of the premaxillary bones, just rostral tothe bony nares, are asymmetrical, the right being severaltimes larger than the left. In adult Ziphius males, there is arostral extension of the right premaxillary sac that is(uniquely) not in contact with the premaxillary bone(Heyning, 1989a). In Tursiops, there are small accessorysacs on the lateral margins of the premaxillary sacs(Schenkkan, 1971; Mead, 1975). In contrast, Ziphius has nowell-defined accessory sacs (Heyning, 1989a). Based onsimple physics, these differences in air sac geometry mayinfluence the mechanical responses of the head toanthropogenic ensonification.Odontocetes have air sinuses surrounding the bonesassociated with hearing; the peribullar and pterygoidsinuses (Figs 8 and 9). These air sinuses arecontinuous with each other (Chapla and Rommel, 2003)and have been described by Boenninghaus (1904) andFraser and Purves (1960) as highly vascularised (seebelow; Fig. 9) and filled with a coarse albuminous foam,which may help these air-filled structures resistpressures associated with depth as well as with acousticisolation. The odontocete larynx is very specialised – itscartilages form an elongate goosebeak (Reidenburg andLaitman, 1987). The laryngeal cartilages fit snugly into thenasal passage and the palatopharyngeal sphincter musclekeeps the goosebeak firmly sealed in an almost verticalintranarial position (Lawrence and Schevill, 1956). Thesemorphological features effectively separate the respiratorytract from the digestive tract to a greater extent than is

J. CETACEAN RES. MANAGE. 7(3):189–209, 2006195Fig. 6. The axial skeletons and rib cages of the domestic dog (a) compared to those of Tursiops (b) and Ziphius (c). The caudal regionof Tursiops has 24-28 vertebrae while that of Ziphius, 19-22, depending on the individual. The neural canals are the dorsal, vertebralbony channels extending from the base of the skull to the tail, in which are contained the spinal cord and associated blood vessels.The ventrally located chevron bones enclose the chevron canal, in which are found the arteries and veins of the caudal vascular bundle.(Redrawn after Rommel and Reynolds, 2002).found in any other mammal (Figs 7b and 7c; Reidenburgand Laitman, 1987). The complex head and throatmusculature manipulates the gas pressures in the air spacesof the head and thus can change the acoustic properties ofthe air spaces and the adjacent structures (Coulombe et al.,1965).The thoracic cavity (Figs 7a and 7b) contains (amongother structures) the heart, lungs, great vessels and incetaceans and sirenians, the thoracic retia (McFarland et al.,1979; Rommel and Lowenstein, 2001). In Tursiops, thecranial aspect of the lung extends significantly beyond thelevel of the first rib (Fig. 7a), in close proximity to the skull(McFarland et al., 1979). The terminal airways of cetaceanlungs are reinforced with cartilage up to the alveoli (Fig. 7d;e.g. Ridgway et al., 1974). Additionally, the cetaceanbronchial tree has circular muscular and elastic sphincters atthe entrance to the alveoli (Fig. 7d; Drabek and Kooyman,1983; Kooyman, 1973; Scholander, 1940). It has beenhypothesised that bronchial sphincters regulate airflow toand from the alveoli during a dive (reviewed in Drabek andKooyman, 1983). Under compression, the alveoli in thecetacean lung collapse and gas from them can be forced intothe reinforced upper airways of the bronchial tree. Thus,nitrogen is isolated from the site of gas exchange, reducingits uptake into tissues and mitigating against potentiallydetrimental excess nitrogen absorption (reviewed in Pabst etal., 1999; Ponganis et al., 2003). The microanatomy ofbeaked whale lungs has not been described and is thereforean area requiring future research.In cetaceans, the ventromedial margins of the lungsembrace the heart (Fig. 7e), so the heart influences thegeometry of the lungs. These single-lobed lungs changeshape with respiration and depth and the heart affects thesize and shape of the lungs because gas distribution in thelungs changes, but the shape of the heart remainsrelatively unchanged. Additionally, because of the mobilityof the ribs, the size and shape of the lungs change in amanner different than do those of a terrestrial animalwith a rigid rib cage and multilobed lung (Rommel,1990). Since respiratory systems contain numerous gas-

196ROMMEL et al.: SOME HYPOTHETICAL CAUSES OF SONAR-RELATED STRANDINGFig. 7. The major respiratory and thoracic arterial pathways are illustrated for Tursiops (a, b). Note the structure of the oesophagus andtrachea (b, c) and the reinforced terminal airways of the cetacean lung with sphincter muscles surrounding the distal bronchioles (d).The lungs with a heart in between (e) are a complex shape that will have different resonant responses to ensonification from a simplespherical model. (a-b adapted from Rommel and Lowenstein, 2001; c-d adapted from Pabst et al., 1999; e adapted from Rommel etal., 2003).filled spaces, the pressure exerted on them at depthaffects their volume, shape and thus their resonantfrequencies. The shapes of compressed cetacean lungs andthe thorax are also influenced by small changes in bloodvolume within the thoracic retia mirabilia (Figs 7e and 10ce; Hui, 1975). Although the thoracic retia have not yet beendescribed in beaked whales, it has been assumed (becausethey are deep divers and their retia are relatively large) thatfilling these retia with blood may have a noticeableinfluence on internal thoracic shape, particularly withdepth.The actions of the liver and abdominal organs pressingagainst the diaphragm, in concert with abdominal musclecontractions, affect gas pressure in and the distribution ofmechanical forces on the lungs. Appendicular-muscledominated locomotors (such as the dog) couple differentsorts of respiratory and locomotory abdominal forces(Bramble and Jenkins, 1993) compared to axial-muscledominated locomotors (such as the cetaceans; Pabst, 1990).This action has not been investigated in cetaceans, but it islikely that it plays some r

Zalophus californianus (e); bottlenose dolphin (f) and the domestic dog,Canis familiaris (g). Each skeleton was scaled proportionately to the beaked whale. TheZiphius skeleton was drawn from photographs of Smithsonian Institution skeleton #504094 and from photographs courtesy of A.

Related Documents:

A Report by the Whale and Dolphin Conservation Society for the First Meeting of the Signatories to the Memorandum . Hector's dolphin, Longman's beaked whale, Perrin's beaked whale, pygmy beaked whale, spade-toothed beaked whale, and fi nless porpoise. It is hoped that this country-specifi c information will assist

Common name of species. Common and scientific names are available at the Departmental . Minke Whale Balaenoptera acutorostrata 500 IC Antarctic Minke Whale, Dark- . Bryde's Whale Balaenoptera edeni 500 IC Blue Whale Balaenoptera musculus EN 500 IC Fin Whale Balaenoptera physalus VU 500 IC Arnoux's Beaked Whale Berardius arnuxii 500 IC

crustacean: a marine animal with a segmented body, shell, and jointed legs. competition pod: a group of male whales competing to mate with a female whale. escort: a male whale swimming close to a female whale in the breeding grounds. fl ukes: the two lobes of a whale’s tail. head lunge: a behavior where a whale lunges forward with its head raised above the water.

Common Name Scientific Name pygmy rabbit Brachylagus idahoensis fisher Pekania pennanti gray wolf Canis lupus . sei whale Balaenoptera borealis fin whale Balaenoptera physalus blue whale Balaenoptera musculus humpback whale Megaptera novaeangliae North Pacific right whale Eubalaena japonica sperm whale Physeter macrocephalus Columbian white .

Toothed cetaceans include the hourglass dolphin (Lagenorhynchus cruciger), long-finned pilot whale (Globicephala melas), the killer whale (Orcinus orca), Southern bottlenose whale (Hyperoodon panifrons), sperm whale (Physeter macrocephalus) and Southern fourtooth whale (Berardius arnuxii). BOX 1

Rough-toothed dolphin Indo-Pacific humpbacked dolphin Dusky dolphin Hourglass dolphin Risso's dolphin Bottlenose dolphin Pantropical spotted dolphin Spinner dolphin Striped dolphin Common dolphin87 Fraser's dolphin Southern right whale dolphin Melon-headed whale Pygmy killer whale False killer whale Killer whale Long-finned pilot whale .

Scientific Name Common Name Non–breeding birds Pygoscelis antarctica chinstrap penguin S Sterna paradisaea Arctic tern S . Balaenoptera musculus blue whale E W M B Balaenoptera physalus fin whale V W Berardius arnuxii Arnoux’s beaked whale W Globicephala melas long–finned pilot whale W

American Math Competition 8 Practice Test 8 89 American Mathematics Competitions Practice 8 AMC 8 (American Mathematics Contest 8) INSTRUCTIONS 1. DO NOT OPEN THIS BOOKLET UNTIL YOUR PROCTOR TELLS YOU. 2. This is a twenty-five question multiple choice test. Each question is followed by